The present invention relates to a screw compressor and more particularly to an oil-free type screw compressor having an oil-free structure in which no liquid lubricant is used in a passage for compressed air, so that it is possible to supply oil-free compressed air.
Since the oil-free type screw compressor does not have a means for reducing heat generated by the compression of the operating gas in a flow passage therefor, a casing which accommodates a male rotor and a female rotor becomes hot. For that reason, the casing is provided with an air cooling fin or a cooling jacket on the outer periphery thereof so as to prevent the casing from becoming extraordinarily hot. JP-A-11-22688 and JP-A-11-33684 disclose that the casing is provided with a cooling jacket on the outer periphery thereof and the industrial water or coolant is introduced in the cooling jacket. Further, in order to eliminate the need for the cooling water, JP-A-1-116297 discloses that the casing is cooled by introducing lubrication oil for lubricating a gear and a bearing into the cooling jacket.
The above conventional oil-free type screw compressor provided with an air cooling fin on the casing, for example, requires a large number of fins to keep a radiation area sufficiently, so that it has a disadvantage that the casing becomes large in order to provide an increased surface area. Further, in the case that the casing is provided with the water cooling jacket, as described in JP-A-11-22688, although there is an advantage that the casing can be efficiently cooled by using a relatively simple means if the industrial water or the like is easily available, it is unsuitable for the case that the industrial water is not easily available. In the case that the industrial water is unavailable, although it is possible to use coolant for the cooling as described in JP-A-11-336684, it is also required to prepare a special solution as coolant and a cooling means for cooling the coolant increased in temperature by the cooling of the casing, thus, it causes a disadvantage that the apparatus is complicated.
On the contrary, an apparatus for cooling the casing with the lubrication oil as disclosed in JP-A-1-116297 uses the lubrication oil, which is necessarily required for the compressor, for its cooling, so that it can advantageously cool the compressor main body easily, even if the industrial water is unavailable.
In the apparatus, the lower the temperature of the lubrication oil for cooling the compressor main body is, the better the cooling efficiency is, while the temperature of the lubrication oil is preferably maintained at about 55xc2x0 C. for lubricating a bearing or a gear, as is an appropriate lubrication oil feeding temperature. Since it is difficult to realize these two types of temperatures by a single oil cooler, the apparatus has been provided with two oil coolers, or the lubrication oil has been cooled down to a temperature at which it is supplied to the cooling jacket, that is, the lower temperature.
In the latter case, the lubrication oil to be fed to a bearing and a gear is excessively cooled to increase mechanical loss, and further, the apparatus necessarily requires a larger-sized oil cooler. This prevents the reduction of the size of a package type of oil-free compressor.
Further, in the conventional oil-free type screw compressors, if casting sand or the like entering the apparatus during the casing manufacturing process remains in the compressor main body or the gear casing, the casting sand is introduced to the bearing or the gear when the lubrication oil is circulated, so that the bearing and the gear may be damaged.
The present invention is provided in view of the above disadvantages of the prior art. It is an object of the invention to provide a reliable oil-free type screw compressor. It is another object of the invention to cool the compressor main body of the oil-free type screw compressor by simple structure. Also, it is an object of the invention to provide a small and inexpensive package type oil-free screw compressor. The present invention attains at least one of these objects.
In order to attain the above objects, according to one aspect of the present invention, there is provided an oil-free type screw compressor comprising a low pressure stage compressor main body and a high pressure stage compressor main body each having a cooling jacket for the cooling by oil; a first passage for supplying the lubrication oil to a bearing and/or a timing gear in each compressor main body; a second passage for supplying the lubrication oil to each cooling jacket for cooling the compressor main body; and an oil sump for accommodating the lubrication oil which has passed through the first or second passage, wherein the lubrication oil passing through the second passage is introduced into the oil sump without passing through the first passage.
In the oil-free type screw compressor, the lubrication oil passing through the first passage may be introduced into the oil sump without passing through the second passage, or the compressor may further comprise an oil cooler capable of cooling the lubrication oil to two different temperatures so that the lubrication oil with the lower-temperature is introduced to the second passage and the lubrication oil with the higher-temperature is introduced to the first passage. Further, a lubrication oil flow passage in the oil cooler may be provided with a branch portion midway thereof so that the lubrication oil with the higher-temperature is supplied from the branch portion.
In order to attain the above objects, according to another aspect of the present invention, there is provided an oil-free type screw compressor comprising a compressor main body provided with a cooling jacket; an electric motor for driving the compressor main body; a gear casing for accommodating a gear set which transmits the rotation of the electric motor to the compressor main body while changing the rotational speed, the gear casing having an oil sump formed in the bottom thereof; an oil pump for feeding lubrication oil from the oil sump to the cooling jacket; an oil cooler for cooling the lubrication oil fed from the oil pump; and a lubrication pipe branching from midway of a lubrication oil flow passage in the oil cooler, thorough which the lubrication oil is supplied to a timing gear and/or a bearing in the compressor main body.
In this oil-free type screw compressor, the compressor may comprise a pipe branching from the lubrication pipe for supplying the lubrication oil to the gear set in the gear casing; the oil cooler may supply two types of lubrication oils with different temperatures; the lubrication oil with the lower-temperature supplied from the oil cooler may be supplied to the cooling jacket; the compressor may comprise a pipe for directly returning the lubrication oil which has cooled the cooling jacket to the oil sump; the compressor may comprise an air cooling fan for cooling the oil cooler by air; the oil pump may be disposed upstream from the oil cooler; the lubrication pipe may be provided with a filter apparatus midway thereof; and the compressor may comprise a return pipe for introducing a part of the lubrication oil, fed from the oil pump, to the gear casing without passing through the oil cooler, and a junction at which the lubrication oil which has passed through the return pipe and the lubrication oil which has passed through the lubrication pipe branching from midway of the oil cooler join.
In order to attain the above objects, according to yet another aspect of the present invention, there is provided an oil-free type screw compressor comprising a compressor main body provided with a cooling jacket; an oil cooler for cooling lubrication oil, through which the lubrication oil is supplied to a lubrication point in the compressor main body and to the cooling jacket; and a branch pipe branching from midway of a lubrication oil flow passage in the oil cooler, thorough which the lubrication oil is supplied to the lubrication point.
In order to attain the above objects, according to still another aspect of the present invention, there is provided an oil-free type screw compressor comprising a compressor main body provided with a cooling jacket; an oil cooler for cooling lubrication oil; and an oil sump for storing the lubrication oil, from which the lubrication oil is supplied through the oil cooler to a lubrication point in the compressor main body and to the cooling jacket, wherein a part of the lubrication oil supplied from the oil sump is supplied to the lubrication point without passing through the oil cooler.
An embodiment of the present invention will be explained below with reference to the drawings.